Meteorisches 10Be in marinen Sedimenten als Tracer für terrestrische Denudationsraten: Eine Machbarkeitsstudie anhand terrestrischer und mariner Sedimente in Zentral-Chile
Zusammenfassung der Projektergebnisse
Knowledge about how fast landscapes erode and the variation of these erosion rates over different time scales yields very important insights into how landscapes evolve and how they respond to changes in climate or tectonics. The volume of continental erosion products that are transferred into the global oceans is an important metric in the calculation of how much CO2 is withdrawn from the atmosphere during weathering. These products of continental erosion are deposited in marine sediment sections. To investigate erosion rates, we developed a new geochemical proxy for continental erosion, the cosmogenic 10Beryllium (Be) to stable 9Be (10Be/9Be) isotope system and tested it on marine sediment offshore from Chile. The cosmogenic nuclide 10Be is formed by cosmogenic irradiation in the Earth’s atmosphere, and its stable 9Be isotope is released from rock by weathering. 10Be travels from the atmosphere into soils mostly by rainfall and in the soil profile it attaches to several components within the soil, where it mixes with 9Be. Slowly eroding areas are characterized by high 10Be/9Be ratios because these isotopes accumulate over time in the soil. Vice versa, if erosion is rapid, low 10Be/9Be ratios in the upper soil layers are found as they are constantly removed by erosion. This isotope system was recently established to calculate erosion rates from entire river catchments. However, when the terrestrial sediment enters the ocean at a river mouth, 10Be contained in the ocean water can chemically attach to the sedimentary material. We were able to show that some chemical components of ocean water (oxides and hydroxides) and their 10Be are rapidly attached to the terrestrially sourced sediment. However, other sediment components, such as clay minerals, seem to reasonably preserve the terrestrial signal. When developed further, this new proxy will be very useful to quantify erosion processes and their variation over time integrated over hundreds to thousands of years. We were very surprised by how rapidly the 10Be from the ocean is increased in the sampled sediment from the terrigenous source to the marine sink and nearly mirrors the open-ocean 10Be concentration just 30 km off the coast. This process has profound impacts on the chemical cycle of 10Be in the ocean.
Projektbezogene Publikationen (Auswahl)
- “Setting the authigenic 10Be/9Be ratio of marine sediment: Implications for deriving the global terrigenous denudation flux from near-coastal sediment”, to be submitted to Geophysical Research Letters
Wittmann, H., von Blanckenburg, F., Christl, M., Mohtadi, M., Bernhardt, A.
(Siehe online unter https://doi.org/10.1002/2017GL074259)
